Variable pitch marine propeller



Jan. 25, 1966 D. J- MARSHALL VARIABLE PITCH MARINE PROPELLER Filed Feb.9, 1965 INVENTOR: DON J. MARSHALL BY My ATTYS,

United States Patent 3,231,023 VARIABLE PITCH MARINE PROPELLER Don J.Marshall, Edgewater, Md, assignor to Goodall Semi-Wetallic Hose & Mfg.(10., Philadelphia, Pa., a corporation of Pennsylvania Filed Feb. 9,1965, Ser. No. 431,251 Claims. (Cl. Mil-160.49)

The present invention relates to marine propellers, and moreparticularly to marine propellers having means for automatically varyingpropeller blade pitch depending upon the thrust requirements of thedriven vessel under varying operating conditions.

Using a fixed blade propeller, the marine designer is seriouslyhandicapped in his attempt to design an all purpose propeller in view ofthe variable conditions which occur during usage of the propeller ondiffering size and designed craft. If the propeller is designed for aparticular craft or vessel, for example of the pleasure boat, cruiserclass variety initially the boat handles excellently, which conditionsoon changes as the boat is used.

The marine architect in selecting a propulsion unit to be mounted in anewly designed hull, calculates the drag or power-consuming factor ofthe hull and selects an engine capable of developing the required powerto move the hull through the water at a selected speed. The marineengineer simultaneously, selects a propeller of the diameter and pitchwhich will most effectively convert that power into useful thrust undervarying water conditions. Some of the factors entering into hiscalculations are: underbody lines; gross weight; displacement at thedesign optimum speed (on plane); hull attitude or trim (weight placementwithin the hull); frictional effects of fouling on the bottom hullsurface; screw placement; and rudder size and position. (For anexcellent article on a comparison of the major methods of marinepropeller design, see Comparing Four Methods of Marine Propeller Design,by Justin H. McCarthy, page 435, vol. 72, A.S.N.E. Journal.)

When the marine engineer bases his calculations on the'above-mentionedfactors as well as others, he is able to predict the performance of thehull surprisingly accurately. However, in the hands of the average boatowner these factors are soon disturbed. For example, added weight in theform of extra equipment, added long range tankage, water absorption bythe hull, overload of passengers and supplies, and their placementwherever space permits causing changes in the center of buoyancy,softening of the bottom finish and growth of marine fouling organismsand other factors add to the power demands and requirements of the hull.Adding to this adverse wind and rough water conditions, the propulsionunit designed by the marine engineer and architect for the specificcraft is no longer in the hull for which it was designed, and a seriousoverload condition exists.

Under these conditions the propulsion unit is forced to operate underconditions of overload, the fuel consumption per mile raises, and as aresult of power output loss, due to impaired breathing and the like, adecrease in the speed of the hull through the water is experienced.

Faced with these problems many boat owners try to find a new propellerfor their vessel or craft. However, due to varying conditions of use,there is no single right propeller for all conditions. All of the hullslowing factors are variables. For example, leisurely cruises sometimesturn into a fast run to shelter in the face of sudden squalls; or afishing trip with one or two passengers presents a different conditionof loading than a family outing of six with hundreds of pounds ofsupplies; or a few hours'running to and from the best fishing grounds asopposed to four or five hours of slow speed trolling; each of theseconditions merit a different screw having a different pitch.

Various cures are illustrated in the prior art, for example, the presetvariable pitch propeller wherein the propeller is set before everyouting based on some kind of guess of the days needs. Other curesillustrated in the prior art include manually variable propellers aswell as supposedly automatic variable propellers. These systems requireconstant attention and have proved economically unfeasible because ofhigh initial costs.

In view of the above, it is an object of the present invention toprovide a variable pitch marine propeller having means to vary the pitchof its blades automatically to suit varying power demands of the hulland engine combination with which it is coupled to provide a high levelof efficiency without overload of the engine.

Another object of the present invention is to provide a variable pitchmarine propeller which changes the pitch of its blades primarily due tochanges of thrust requirements so as to provide the pitch angle whichwill produce the maximum thrust under existing water conditions.

Another object of the present invention is to eliminate the fixed ratiowhich exists between hull speed and engine r.p.m. by providing anautomatically variable pitch marine propeller.

Still another object of the present invention is to provide anautomatically variable pitch marine propeller which will develop all ofthe desirable features of pitch variation automatically, at a lowerinitial cost, while effecting economies in operation.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying drawing in which:

FIG. 1 is a side elevation of an exemplary pleasure craft havingportions thereof broken away to more clear ly illustrate apparatus usedin conjunction with the propeller of the present invention;

FIG. 2 is an enlarged fragmentary view of a portion of a variable pitchmarine propeller constructed in accordance with the present invention;

FIG. 3 is a fragmentary sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a fragmentary sectional view taken along line 44 of FIG. 3;and

FIG. 5 is a fragmentary 'view of the device of the present invention andillustrating the propeller in a different position from the positionshown in FIG. 2. Referring now to the drawing, and especially FIG. 1, apleasure craft or boat 10 having a prime mover or engine 11 mountedwithin the hull 12 of the boat It is connected via a line shaft 13,supported by line bearing 14 and strut bearing 15, to a variable pitchpropeller 20. Just beneath the stern of the boat It), and aft of thepropeller 20, is a conventional rudder 16. Although the principle ofoperation of the propeller 20, as hereinafter described, is related to aboat having an inboard engine, it should be recognized at the outsetthat the variable pitch propeller of the present invention may be usedin conjunction with outboard engines.

In accordance with the invention, the propeller 20 is provided withmeans to enable accommodation of the propeller to the varying thrustrequirements of the hull 12. To this end, a shaped collar 21, in thepresent instance shaped in the form of a hexagonal parallelepiped withopposite parallel edges of unequal length, is mounted on and connectedto the line shaft 13 just aft the strut bearing 15 and spaced from atail stock 22 which is connected to the extended terminus of the lineshaft 13 by,

' in the present instance, a bolt 23. As illustrated inthe drawing, thepropeller assembly 20 comprises a hub 24 having a hollow frontal portion25 and an after solid portion 26, coaxially mounted on the shaft 13 andaxially movable between the tail stock 22 and the collar 21, Which actsadditionally as a stop to limit forward axial movement of the hub. Thehub 24 is keyed to the line shaft 13, in the present instance by afrontal plate 27 connected to the hub by bolts 28, and having a shapedaperture 29 to en gage the shaped collar 21 thus permitting rotation ofthe hub with the shaft 13.

Mounted circumferentially of the hub are a plurality ofcircumferentially spaced, radially projecting blades 30, each having anaxle 31 extending into the hollow frontal portion 25 of the hub 24 androtatably journalled thereto. The blades 30 may be of conventionalmarine design of the type normally found on pleasure craft and the like.However, preferably, in order to avoid undesirable reactions or momentson the blades when moving through the water, it is desirable that theaxles 31 of the blades 30 be positioned at or along a line through thecenter of pressure of the resultant working section of the blade. Inaeronautics, this point is sometimes referred to as the center of lift,but at any rate means the point in the chord of an airfoil section,prolonged if necessary, which is at the intersection of the chord andthe line of action of the resultant water or air force.

In order to permit automatic adjustment of the blades 30 about theiraxles 31 dependent upon the thrust necessary to propel the craft throughthe water, means are provided interiorly of the hub to increase thepitch of the blades as thrust demands are increased. To this end,interiorly of the hub and mounted in the present instance on theterminus of each axle 31, is a lever arm 32 (see FIG. 4) having aleading and trailing edge 33 and 34. Each of the levers has a first camportion 35 on the leading edge 33 and spaced longitudinally of thelever, a second cam portion 36 on the trailing edge 34 thereof. In thepresent instance the first cam portion 35 of each lever arm 32 isaligned axially of the line shaft 13 with a portion 37 of the collar 21,for purposes which will hereinafter be explained. In the after solidportion 26 of the hub 24, mounted in bored holes 39 and aligned with thesecond cam portion 36 of each lever arm 32, is thrust reaction orbiasing means, in the present instance comprising compression springs38.

In operation, the biasing means or spring 38 engages the second cammingportion 36 of the lever arm 32, which tends to maintain the blade 30associated therewith at its finest pitch angle, such as illustrated inFIG. 2. As the blades commence rotation, in the counterclockwisedirection as viewed in FIG. 3, and increased thrust demands are made ofthe propeller 20, the hub 24 moves axially of the shaft against thecollar 21 causing bearing means 37 on the after side of the collar 21 tobear against the first cam portion 35 thereby causing rotation of eachblade about its axle 31. As may be seen in FIG. 5, as thrust'demands areincreased to a maximum, the second cam portion 36 moves against thespring 38 until the spring is fully compressed and the hub 24 is forwardagainst the collar 21. In this position the blades are at their maximumpitch angle and attempt to move the boat through the water the maximumamount for each revolution of the shaft 13.

In practice the spring pressure rates of the springs 38 can be madelinear or curvilinear so as to more closely match the torque curve of aparticular engine for a particular boat. One of the advantages of theabove-(la scribed arrangment of the biasing means or springs is that thesprings do not have to be closely matched in manufacture as the bladesare effectively coupled together via the hub, levers and collar.

The manner in which spring force for a single blade may be calculatedis: Spring force developed thrust+ No. of blades+distance from thecenter of an axle to the second cam portion/distance from the center ofthe axle to the first cam portion. For example, assume a HP. enginedevelops 900 lbs. thrust at full power and a three-bladed propeller isprovided on the shaft of the engine. Further assume that the ratio ofdistances of the second cam portion to the first cam portion from thecenter of the axles is 3/1. Spring force (force to close thespring)=9-00 lbs/3 blades/M1 lbs.

Many existing outboard and inboard propellers are provided with slipclutches which prevent damage to the propeller blades by effecting slipbetween the blades and the prime mover upon the blades striking a hardobject. The conventional slip clutch normally comprises a compressedsleeve or disk of rubber mounted between the drive shaft and the hubconnecting the blades, which compressed rubber is capable of movementrelative to the hub if a blade associated with the hub strikes, forexample, the sandy bottom or other objects impeding the free rotation ofthe blades through the water.

The variable pitch marine propeller of the present invention lendsitself for easy adaptation of a slip type clutch which may be mounted ineither the tail stock or forward of the hub. For example, if a slipclutch were to be mounted in the tail stock, a slip clutch couldcomprise a pair of concentrically mounted radially spaced sleeves, theinner sleeve being secured to the shaft extension and the outer sleevesplined or connected to the after portion of the hub. Between the innerand outer sleeve a compressed sleeve of rubber is mounted, which sleeveof rubber affords driving connection between the shaft extension and theouter sleeve thus affording rotation of the hub. Of course in anarrangement such as above described, the collar mounted forward of thehub would preferably be circular in cross section thus providing nokeying of the collar to the hub, rotation being caused solely by theconnection of the hub to the aforementioned outer sleeve.

Thus, at slow speeds such as when trolling or the like, when thrustrequirements are at a minimum, the propeller pitch will be automaticallysuited for slow speed, minimum thrust requirements, i.e. a fine pitch.0n the other hand, when the boat is being subjected to increased dragconditions, such as when cruising at high speeds, thrust requirementsare increased and. accordingly, the blades of the propeller will attainautomatically a pitch best suited for existing requirements. The resultis that the pitch of the blades is automatically adjusted to accommodateany water state, hull condition and speed of hull.

Although the invention has been described with a certain degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction and combination and arrangement of parts may be madewithout departing from the spirit and scope of the invention ashereinafter claimed.

What is claimed is:

1. In a boat having a hull and a prime mover carried thereon, a lineshaft connected to said prime mover at one end and extending exteriorlyof the hull and terminating in a tail stock, a variable pitchedpropeller mounted on said shaft adjacent said tail stock; a shapedcollar mounted on and connected to said shaft and spaced from said tailstock, said propeller comprising a hub, having a hollow portion and asolid portion, axially movable on said shaft between said tail stock andsaid collar and keyed to said shaft to rotate therewith,circumferentially spaced, radially projecting blades each having an axleand extending into the hollow portion of said hub and rotatablyconnected thereto, a lever having a leading and a trailing edge, securedto each of said axles interiorly of said hub in said hollow portion,each of said levers having a first camming portion on said leading edgeand a second camming portion on said trailing edge, thrust reactionmeans in said solid portion of said hub for engaging said second cammingportion and means on said collar to engage said first camming portionwhereby upon rotation of said shaft the resulting thrust from said bladerotation causes said hub to move axially of said thrust rotating saidblades about their axles until said thrust reaction means force equalsthe thrust on said hub.

2. Apparatus in accordance with claim 1 wherein said blades are mountedon their axles along a line through the center of pressure of saidblades.

3. Apparatus in accordance with claim 1 wherein said thrust reactionmeans comprises a spring.

4. Apparatus in accordance with claim 3 wherein said spring has acurvilinear pressure rate closely approximating the torque curve of saidprime mover.

5. Apparatus in accordance with claim 1 wherein said hub is mountedcoaxially of said shaft and contains means References Cited by theExaminer UNITED STATES PATENTS Kellogg et al 170--160.49 Bellman170-160.51 Irgens 170164.54 Bugatti 170-160.53 Miller 170-16049 Gansert170-160.59 X Coleman 170-16053 Italy.

defining a shaped aperture to receive and engage said 15 JULIUS E. WEST,Primary Examiner.

collar therein.

1. IN A BOAT HAVING A HULL AND A PRIME MOVER CARRIED THEREON, A LINESHAFT CONNECTED TO SAID PRIME MOVER AT ONE END AND EXTENDING EXTERIORLYOF THE HULL AND TERMINATING IN A TAIL STOCK, A VARIABLE PITCHEDPROPELLER MOUNTED ON SAID SHAFT ADJACENT SAID TAIL STOCK; A SHAPEDCOLLAR MOUNTED ON AND CONNECTED TO SAID SHAFT AND SPACED FROM SAID TAILSTOCK, SAID PROPELLER COMPRISING A HUB, HAVING A HOLLOW PORTION AND ASOLID PORTION, AXIALLY MOVABLE ON SAID SHAFT BETWEEN SAID TAIL STOCK ANDSAID COLLAR AND KEYED TO SAID SHAFT TO ROTATE THEREWITH,CIRCUMFERENTIALLY SPACED, RADIALLY PROJECTING BLADES EACH HAVING AN AXLEAND EXTENDING INTO THE HOLLOW PORTION OF SAID HUB AND ROTATABLYCONNECTED THERETO, A LEVER HAVING A LEADING AND A TRAILING EDGE, SECUREDTO EACH OF SAID AXLES INTERIORLY OF SAID HUB IN SAID HOLLOW PORTION,EACH OF SAID LEVERS HAVING A FIRST CAMMING PORTION ON SAID LEADING EDGEAND A SECOND CAMMING PORTION ON SAID TRAILING EDGE, THRUST REACTIONMEANS IN SAID SOLID PORTION OF SAID HUB FOR ENGAGING SAID SECOND CAMMINGPORTION AND MEANS ON SAID COLLAR TO ENGAGE SAID FIRST CAMMING PORTIONWHEREBY UPON ROTATION OF SAID SHAFT THE RESULTING THRUST FROM SAID BLADEROTATION CAUSES SAID HUB TO MOVE AXIALLY OF SAID THRUST ROTATING SAIDBLADES ABOUT THEIR AXLES UNTIL SAID THRUST REACTION MEANS FORCE EQUALSTHE THRUST ON SAID HUB.